Crystal oscillator frequency stabilization system



Nov. 29, 1966 CRYSTAL OSCILLATOR FREQUENCY STABILIZATION SYSTEM Filed Sept. 2l, 1964 R. N. LONGUEMARE, JR., ETAL 5 Sheets-Sheet l INVENTORS. ,e/v. aA/Mama; fr. BY/f. 4. fie/5515 NOV- 29 1966 R. N. LONGUEMARE, JR.. ETAL. 3,289,096

CRYSTAL OSCILLTOR FREQUENCY STABILIZATION SYSTEM Filed Sept. 2l, 1964 5 Sheets-Sheet 2 INVENTORS. ,e Af. amaai/ms; Je BY H. :6e/5&5

KWM

NOV 29 1966 R. N. LQNGUEMARE, JR., ETAL. 3,289,096

CRYSTAL OSCILLATOR FREQUENCY STABILIZATIQN. SYSTEM Filed Sept. 2l, 1964 3 Sheets-$116912 5 United States Patent O 3,289,096 CRYSTAL OSCILLATOR FREQUENCY STABILIZATION SYSTEM Robert Noel Longuemare, Jr., Ellicott City, and Halsey L. Tribble, Glen Burnie, Md., assignors, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed Sept. 21, 1964, Ser. No. 398,136 2 Claims. (Cl. 331-1) The present invention is generally related to frequency stabilization and more particularly to a system for stabilizing the instantaneous frequency of a high quality, crystal controlled oscillator circuit.

It is commonly recognized by radar systems design engineers that hi-gh performance lDoppler radar systems require one or more highly phase-stable yfrequency references. For these systems short term or instantaneous stability is most critical, as opposed to the more common requirement for long term stability.

Consideration of devices of the prior art indicates that the best type of freguency reference presently known for application in such radar systems is a high quality crystal controlled oscillator. The present invention -was created to further improve and stabilize the performance of high quality crystal controlled oscillators to provide .an ultra phase-stable frequency reference. The invention also provides for frequency or phase modulation of the output signal in applications Where such modulation would Abe desirable.

To att-ain this high degree of phase stability, the present invention utilizes a conventional crystal controlled oscillator circuit having a Vernier frequency control element to provide the input signal to the succeeding elements of the stabilization system. A portion of this input signal is applied, through a resistive attenuator pad for purposes of isolation and :a 'buffer l.amplifie-r, to la phase shift circuit utilizing a high Q `qua-rtz crystal series resonator in which the series resonant lfrequency of the crystal is selected to :be identical -to the frequency to be produced by `the oscillator lto Ibe stabilized. 'The output signal provided by this series resonator phase shift circuit remains in phase with its input sign-al, from the oscillator to be stabilize-d, so long las that input signal is .at the selected resonant frequency, but if the oscillator has allowed this frequency to drift slightly, the phase of this output signal will ,be shifted due to the 'frequency-phase character-istie of this phase shift circuit. This output signal from the series resonator phase shift circuit is then passed thro-ugh an amplifier-limiter circuit, which is also tuned to the Idesired oscilla-tor reference frequency, for amplification and .removal of any undesired amplitude :modulation components. The signal is then provided as a first input to a Iphase detector circuit. A phase reference signal is provided as a second input to the detector circuit by pass-ing la portion of the output signal from the oscillator through a variable phase shifter which has been adj-usted to provide a xed phase shift of ninety degrees to any signal passed therethrough. This phaseshifted reference signal is then passed lthrough a tuned amplifier-limiter circuit identical to that previously mentioned, and coupled to the phase detector circuit. This phase detector Icircuit produces zero output voltage when the two input signals thereto are exactly ninety degrees apart in time phase. For any other phase difference therebetween, it produces `a direct current (D.C.) Voltage proportional t-o the angular deviation from this ninety degree reference point. This -D.C. voltage Iis passed through a D.C. amplifier controlled in such manner :as to maintain a stable control loop and is then applied to the terminal coupled to the Vernier frequency control element of the crystal controlled oscillator causing `the oscillator freice quency t-o be varied in 4a direction to reduce the phase detector output voltage to zero, which will occur when the oscillator frequency is returned .to its precise -design frequency. A summation point is provided between the phase detector circuit and the D.C. :amplifier xfor injection of a modulation command signal if phase or frequency mod lation of the output signal is desired in a particular application.

An object of the present invention is the provision of a frequency reference system.

Another object is to provide :a system for stabilizing the instantaneous frequency of an oscillator circuit.

A further object of the invention is the provision of an ult-ra phase stable frequency reference system.

Still .another object is to provide a phase stabilized, high quality, crystal controlled oscillator frequency reference system.

Yet another object of the present invention is the provision of a phase stabilized, high quality, crystal controlled 'oscillator frequency reference system having provision for modulation of its output signal.

Other objects and features -of the invention will become apparent to those .skilled in the `art as the disclosure is revealed in the following detailed description of .a preferred embodiment of the invention vas illust-rated in the accompanying sheets of drawing in which:

FIGURE l is :a block diag-ram of the invention showing the relative association of the various component circuits within the overall system; p

'FIGURE 2 Idiscloses one embodiment of a crystal controlled oscillator Asuitable `for use in block 111 of FIG- UR=E l;

FIGURE 3 shows an embodiment of -a buffer amplilier of a type suitable for util-ization in block 113 of FIGURE l;

FIGURE 4 discloses a schematic embodiment of a crystal phase shift circuit suitable for use in` block 114 of FIGURE l;

FIGURE 5 depicts schematically an embodiment of a tuned `amplifier yand limiter circuit suitable 'for use in blocks 115 and 118 :of FIGURE L1;

FIGURE `6 presents in schematic form -a suitable embodiment of a phase detector circuit for use in block 116 of FIGURE 1;

FIGURE 7 discloses a suitable embodiment of a variable phase shift circuit for utilization in block 117 of FIGURE l;

FIGURE 8 shows a schematic embodiment of a D.C. .amplifier :and feedback network ysuitable for use in block 121 of FIGURE l;

FIGURE 9 depicts the relationship of phase shift t-o changes in frequency as a signal is passe-d through `a series crystal phase shift circuit such as that shown in FIG- URE 4;

FIGURE 10 represents the relationship of the amplitude of `an output signal from a series crystal circuit, such Ias that shown in 'FIGURE 4, to ythe frequency of the applied input signal, wherein fs represents the resonant frequency of the series crystal; and

FIGURE l1 depicts the characteristic curve of a phase detector circuit such as ythat shown in FIGURE 6, representing the D.C. output volta-ge of such la circuit as a function of the difference in relativephase shift in deg-rees between la reference signal yand an input signal to be compared therewith.

Referring now to the drawings, wherein like reference characters designate like or corresponding parts throughout the several figures, there is shown in the embodiment of FIGURE .1, a controlled crystal oscillator 111 which has its output terminal coupled to a resistive attenuator pad 112, of a type common in the art, for isolation pur poses. Attenuator 112 is coupled through a buffer amplifier 113, many of which are common in the art, which increases the power level of the signal provided to a following crystal phase shift circuit 114. This crystal phase shift circuit, a suitable embodiment thereof being shown in FIGURE 4, provides an output signal which is in phase -With the input signal applied thereto so long as the frequency of that input signal is equal to the series resonant frequency (fs) of the crystal therein; however, deviation fromthis resonant frequency by the input signal causes the output signal to be shifted in phase in proportion to such frequency deviation. This output signal is applied ,via .a tuned amplier and limiter circuit 115 which amplies the signal and removes any undesired amplitude modulation components thereon. Amplifier 115 is coupled to a first input terminal of a phase detector circuit 116, which has a second input terminal to which a phase reference signal is applied. That reference signal is created by coupling the output terminal of crystal oscillator 111 to a variable phase shifting circuit 117, many of which are common in the art, which has been adjusted to provide a signal at its output terminal that is shifted ninety degrees in phase from that applied to its input terminal. The output from phase shift circuit 117 is coupled through a tuned amplifier and limiter circuit 118 of the same type as circuit 115, many-of which are common in the art and a suitable embodiment thereof being shown in FIGURE 5, to the second input terminal of phase detector 116 to provide the reference signal thereto. a suitable embodiment of which is shown in FIGURE 6, maintains a zero volts output signal so long as the input signal applied to its iirst terminal differs in phase by ninety degrees from the reference signal applied to its second terminal; however, if-the phase difference between these two applied signals deviates from ninety degrees, phase detector 116 will provide a D.C. output voltage proportional to this deviation. The output terminal of phase detector 116 is coupled through a summation or connection point 119 to a D.C. amplifier network 121, an embodiment of which is shown in detail in FIGURE 8, whose frequency response is controlled in order to maintain a stable control loop. An input terminal 120 is coupled to summation point 119 to provide a path for a modulationvinput signal if it is desired to modulate the signal generated by oscillator 111. The output terminal of amplier 121 is coupled to the input voltage control terminal of oscillator 111. The stabilized oscillator output signal provided by the invention is available at output terminal 122, which is coupled to the output terminal junction of oscillator 111.

FIGURES 2 through 8 disclose detailed embodiments of circuitry suitable for use in various blocks of the invention as shown in FIGURE l. It is believed that circuitry suitable for use in each of the blocks shown in FIGURE l may be found in the prior art. Accordingly, the novelty of the present invention is believed to lie in the combination of these individual blocks to provide a unique system for stabilizing the instantaneous frequency of an oscillator. Therefore, the embodiments in FIG- URES 2 through 8 will be discussed with regard to their individual functions and information will be provided to enable construction thereof, but a detailed discussion of the various components comprising each of the embodiments appears unnecessary and will not be undertaken.

FIGURE 2, an embodiment of a voltage controlled, crystal oscillator circuit suitable for use as block 111 in FIGURE 1, provides at its output terminal a relatively fixed-frequency signal which is to be further stabilized by the invention. The frequency of this signal is primarily determined by the resonant frequency of the crystal" 213, the choice of which is determined by the frequency which the invention is desired to produce. An input terminal for receiving a control voltage is coupled via a coil 214 to a varactor control diode 212, the capacitance of which may be varied by a control voltage resulting in a pro- Phase detector 116,

portional change in the frequency provided by the oscillator at its output terminal. The following types and values of components and potentials have been tested and found satisfactory for comprising the circuitry of FIG- URE 2:

Transistor 211 2N1505.

Element 212 Varactor. Crystal 213 Selected (41.8 me. used in test). Inductances 214, 217,

and 21S 22 microhenries. Inductance 215 2.2 microhenries. Inductance 216 .4l microhenry. Capacitance 219 180 picofarads. Variable capacitance 220 7 to 45 picofarads.

Capacitances 221, 222, l

223, 224, and 226 1000 picofarads.

Capacitance 225 8 microfarads. Resistance 227 2200 ohms. Resistance 228 390 ohms. Resistance 229 180,000 ohms. Resistance 230 2000 ohms. Resistance 231 100,000 ohms.

D.C. potential source 232 -45.volts.

FIGURE 3 is an embodiment of a buffer amplifier suitable for use as block 113 in FIGURE 1, and the following types and values of components and potentials have been tested and found satisfactory for use therein:

Transistor 311 2Nl505. Inductance 312 1.5 microhenries. Inductance 313 1 microhenry. Inductance 314 22 microhenries. Inductance 315 .63 microhenry. Element 316 Transformer. Variable capacitance 317 4 to 30 picofarads. Capacitances 318, 321, 322,

323, 324, and 325 1000 picofarads. Variable capacitance 319 1.5 to 7 picofarads. Resistance 326 30 ohms. Resistance 327 20 ohms. Resistance 328 2,200 ohms. Resistance 329 2,000 ohms. Resistance 331 390 ohms.

D.C. potential source 332 -45 volts.

In the crystal phase shift circuit of FIGURE 4, which may be utilized las block 114 of FIGURE l, is shown a crystal 411. The series resonant frequency fs of thisv crystal is selected to correspond to the frequency which the stabilized system of the invention is intended to provide and if good long term stability is desired or necessary, this crystal should be enclosed within a crystal oven in the usual manner. An input signal of frequency f5 when applied to the circuit of FIGURE 4 will be passed to its output terminal without a shift in phase; however, any input signal which deviates from that frequency will be shifted in phasel as it passes therethrough in proportion to the amount of frequency deviation. The following types and values of components have been tested and found satisfactory for use in this embodiment:

Crystal 411 A-T cut, High Q, 3rd

overtone, fs=41-8 mc.

Inductance 412 22 microhenries.

Inductance 413 Selected.

Variable capacitance 414 7 to 45 picofarads.

Resistance 415 20 ohms.

Resistance 416 39 ohms.

Resistance 417 91 ohms.

FIGURE 5 shows an embodiment of a tuned amplifier and limiter circuit suitable for use as blocks 115 and 118 of FIGURE 1. The `amplifier is tuned to the frequency fs which the system is constructed to provide, and the limiting portion of the circuit removes undesired amplitude modulation components from the amplified signal as it is passed therethrough. This embodiment has been constructed and satisfactorily tested utilizing the following types and values of components:

Tube 511 5702.

Tube 512 5639.

Element 513 Transformer. Inductance 514 RF coil. Inductance 515 RFcoil. `Capacitances 516, 521, S22, and 523 1000 picofarads. Capacitance 517 1 pic-ofarad. Capacitance 518 100 picofarads. Capacitance 519 470 picofarads. Resistance 524 270 ohms. Resistance 525 20,000 ohms. Resistance 526 2,200 ohms. Resistance 527 110 ohms. Resistance 528 680 ohms. Resistance S29 6,500 ohms.

In FIGURE 6 a suitable embodiment of a phase detector circuit for use as block 116 of FIGURE 1 is shown, in which one input signal is applied to a first terminal via a coupling capacitance 631 and a second reference input signal is applied to a second input terminal via a coupling capacitance 629. So long as the time phase difference between these two input signals remains at ninety degrees, the output terminal couplied to the inductance 626 will be maintained at a D.C. potential of zero volts. However, should the time phase difference between the two input signals become greater than or less than ninety degrees, a DC. potential proportional to this deviation from a ninety degree difference will be produced by the phase detector circuit and provided, via inductance 626, at its output terminal. The following types and values of components have been utilized in the construction and satisfactory testing of this embodiment:

All diodes (611-623) 1N914.

Elements 624 and 625 Transformers. Inductance 626 RF coil.

Variable capacitances 627 and 628 1.5 to 7 picofarads. Capacitances 629 and 631 1000 picofarads. Capacitances 632 and 633 picofarads. Resistances 634 and 635 100,000 ohms. Potentiometers 636 and 637 0-500 ohms. Resistance 638 10,000 ohms. Terminals 639 and 641 Test points.

The embodiment of a variable phase shifter as shown in FIGURE 7 is suitable for use as block 117 of FIGURE 1 when it is adjusted to provide la ninety degree shift in time phase to all signals passed therethrough. Suitable component types and values have been found to include the following:

Element 711 Transformer. Variable capacitance 712 7 to 45 picofarads. Resistances 713 and 714 510 ohms.

In FIGURE 8 a D.C. amplifier `and feedback network, suitable for use as block 121 of FIGURE 1, has its input terminal coupled via a resistance 821 to a transistor 811 and its output terminal coupled from transistor 814 to subsequent circuitry. The circuit ampliiies the D.C. control signal passed therethrough. The following types and values of components and potentials have been tested and found satisfactory for use therein:

Transistors 811, 812, 813, and 814 2Nl547.

Capacitances 815 and 816 22 microfarads. Capacitance 817 180 picofarads. Capacitance 818 `3300 picofarads. Capacitance S19 4700 picofarads. Resistance 821 2000 ohms. Resistance 822 100,000 ohms. Resistance 823 1000 ohms. Resistance 824 35,000 ohms.

Potentiometer 825 0-10,000 ohms. Resistances 826 and 827 7,500 ohms. Resistance 82S 15,000 ohms. Resistance 829 5,100 ohms. Resistance 831 46,000 ohms. Resistance 832 200 ohms. Resistance 833 1000 ohms. Resistance 834 47,000 ohms. Resistance 835 20,000 ohms. Resistance 836 10,000 ohms. D.C. potential source 837 -45 volts.

D.C. potential sources 838 and 839 +45 volts.

In FIGURE 9 is shown the frequency-phase shift relationship of a signal as it is passed through a crystal phase shift circuit of the type to be utilized as block 114 of FIGURE l (a suitable embodiment thereof being shown in FIGURE 4). The curve indicates that `as the frequency of the applied signal deviates from the resonant frequency fs for which the circuit is constructed, the time phase shift imparted to the signal as it passes through the circuit increases rapidly from zero at fs, to a proportional positive or negative shift on either side of fs.

The curve of FIGURE 10 indicates the relationship of the relative amplitude of the signal which will be passed by a crystal phase shift circuit such as block 114 of FIGURE 1 to the deviation of that signal `from the resonant frequency fs for which the circuit is designed. The curve shows that the greatest-amplitude possible for an output signal Will occur when the applied signal has the exact frequency fs, and that the amplitude declines rather rapidly for signals whose frequencies deviate from fs.

The curve of FIGURE 11 represents the relationship between phase difference and the D.C. output voltage of a phase detector circuit such as that utilized in block 116 (a suitable embodiment of which is shown in FIG- URE 6). The curve indicates that so long as the relative time phase difference between an input signal and a reference signal, applied to a detector such as that in block 116, remains at ninety degrees the D.C. output signal produced by the detector circuit will remain at zero volts; however, when this relative time phase difference deviates from ninety degrees, the D.C. output signal will become a positive or negative voltage Whose magnitude is proportional to the amount of deviation.

A suitable embodiment of the invention as depicted in FIGURE 1 has been constructed and satisfactorily tested utilizing the various component embodiments shown in FIGURES 2 through 8. For this test the stabilized frequency to be produced by the invention was 41.8 megacycles (mc.) per second, and the attenuator pad 112 of FIGURE 1 was constructed to provide an attenuation of six decibels.

It is to be understood that these particular embodiments, components, values, and frequencies are presented only for illustrative purposes and are not intended to limit the scope of the invention in any Way.

OPERATION The operation of the invention occurs in the following manner. It is assumed that oscillator 111, phase shift -circuit 114, and tuned amplifier circuits and 118 have been previously prepared (i.e. constructed and/or adjusted) to produce the particular frequency Afs which the invention is intended to' provide, in ultra stabilized form, at output terminal 122. Initially oscillator 111 provides at its output terminal a signal of relatively stable frequency is which is passed via isolating attenuat-or pad 112 and buffer amplifier 113 to phase shift circuit 114. If the signal presented to phase shift circu-it 114 is being -maintained precisely at the desired frequency fs by oscillator 111, that signal Will be permitted to pass through -circuit 114 without introduction of any phase shift thereby (as indicated by the curve of FIGURE 9) and at maximum amplitude (as indicated by the curve of FIG- URE however, if the frequency of the signal being produced by oscillator 111 has deviated slightly from the desired frequency f5, this signal will be shifted in phase as it passes through circuit 114 in proportion to the amount of this frequency deviation, and the amplitude of the signal will be decreased (see FIGURES 9 and 10). The signal is then applied to tuned amplifier and limiter circuit 115. This circuit, which is tuned to frequency fs, amplifies the signal while the voltage limiter portion thereof removes any undesired amplitude modulation components from the signal. The signal is then applied as a first input signal to phase detector 116. The phase detector 116 has a second input, or reference, signal applied thereto which is obtained by passing a portion of the output signal of oscillator 111 through a phase shifter 117 which has been adjusted to provide a ninety degree shift in time phase to any signal passing therethrough. The output of ninety degree phase shifter 117 is then passed through tuned amplifier and limiter circuit 118 and applied as the reference signal to detector 116.

Phase detector 116 compares the time phase difference between the signal applied to its first input terminal which has been passed through crystal phase shift circuit 114, and the reference signal applied to its second input terminal; so long as this time phase difference is exactly ninety degrees (indicating that the frequency of the signal being produced by oscillator 111 is precisely the desired lfrequency fs because if it were not, the signal applied to the first input terminal would have been shifted in time phase in passing through crystal phase shift circuit 114 by an amount proportional to the deviation from that frequency), the D C. output voltage produced by phase detector 116 will remain at zero volts. However, if this time phase difference is greater than, or less than, ninety degrees (which will result when the phase shift circuit 114 introduces a phase shift proportional to any deviation of the signal from the desired frequency fs), the D.C. output voltage produced by phase detector 116 will no longer be zero, but will become a voltage proportional to the deviation, in relative time phase, from ninety degrees, as indicated by the phase detector characteristic curve shown Yin FIGURE 11. This D.C. output voltage of detector 116 is passed through D.C. amplifier and feedback network 121 and provided to the input voltage control terminal of oscillator 111. This D.C. Voltage is applied to a vernier control element within oscillator 111 which is capable of causing the oscillator to vary in frequency in an amount and direction sufficient to cause the oscillator to return precisely to lthe desired frequency fs, which then becomes the stabilized output frequency provided to output terminal 122, for application in other circuitry. A suitable embodiment of an oscillator for use in block 111 of FIGURE 1, as shown in FIGURE 2, utilizes a varactor diode 212 as the Vernier control element. The D.C. control voltage applied to the varactor diode results in a change in its effective capacitance thereby varying the oscillator frequency to return it precisely to the desired frequency fs, at which time the phase shift formerly introduced in the Acontrol loop by phase shift circuit 114 will decrease to zero, causing the time phase difference present at detector circuit 116 to return to ninety degrees and its D.C. output voltage to return to zero. Once in operation, the invent-ion constantly guards against, and if necessary compensates for, any deviation by oscillator 111 from the desired frequency fs, thus providing an ultra stable frequency reference signal'at output terminal 122.

Input terminal 120 and summation point 119 are provided at the input terminalof D C. amplifier 121 as an optional feature, and may be utilized for injecting a modulation command signal if a particular application should make such modulation desirable. An audio frequency input signal may be applied at a moderately low level to terminal 120, and this will result in direct frequency modulation of the output signal. Phase modulation may '8 be just as readily obtained by passing the' audio signal through an appropriate filter network prior to application at terminal 120.

Thus it becomes apparent from the foregoing description and annexed drawings that the invention, an ultra precise oscillator 'phase stabilization system, is a useful and practical device having many applications in the lield of electronics.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

We claim:

1. An electronic oscillator stabilization system for providing an output signal having a high degree of frequency and phase stability comprising:

a high quality crystal controlled transistor oscillator means having output means for providing a frequency controlled output signal, and having input means for receiving a signal for regulating a solid state varactor diode element which comprises a vernier frequency control element in said oscillator means;

an electrical attenuation means having input and output terminal means, said input terminal means being coupled to said output means of said electronic oscillator means;

a buffer amplifier means having input and output means,

said input means thereof being coupled to said output terminal means of said electrical attenuation means for receiving a signal from said oscillator means therethrough;

a series crystal phase shifting means comprising a first phase shifting means for sensing any deviations from a predetermined frequency in signals passing therethrough and introducing a phase shift in said signals proportional to said deviations in frequency, said phase shifting means having input and output means, said input means thereof being coupled to said output means of said buifer amplifier means;

a first tuned amplifier and limiter means having input and output means, said input means thereof being coupled to said output means of said first phase shifting means;

a second phase shifting means for introducing a phase shift of predetermined amount into any signal passed therethrough, having input and output means, said input means thereof being coupled to said output means of said oscillator means;

a second tuned amplifier and limiter means having input and output means, said input means thereof being coupled to said output means of said second phase shifting means;

a phase detector means having a first input means coupled to said output means of said iirst tuned amplifier and limiter means for receiving a rst signal therefrom, having a second input means coupled to said output means of said second tuned amplifier and limiter means for receiving a reference signal therefrom, and having an output means coupled to said input means of said oscillator means for providing thereto a direct current potential proportional to the amount of deviation from a predetermined relative phase difference between said first signal and said Vreference signal, to regulate said Vernier frequency control element within said oscillator means thereby causing said' oscillator means to maintain a very stable frequency output signal; and

an output terminal means coupled to said output means of said oscillator means, to provide said very stable frequency output signal thereat for utilization in subsequent circuitry.

2. An electronic oscillator stabilization system for 3,289,096 9 providing an output signal having a high degree of frequency and phase stability comprising:

a high quality crystal controlled transistor oscillator -viding thereat a direct current potential proportional to the amount of deviation from a predetermined relative phase difference between said first signal and means having output means for providing a frequency said reference signal;

controlled output signal, and having input means a direct current amplifier and feedback means to profor receiving a signal for regulating a solid state Vide controlled amplification of a. direct current sigvaractor diode element which comprises a Vernier nel, haVng input Ineens COupled tO said Output means frequency control element in said oscillator means; of said phase detector means for receiving therefrom an electrical attenuation means having input and out- Said direCt Current potential, and haVng Output meanS put terminal means, said -input terminal means being 10 Coupled tO Said input Ineens 0f Said OSCllatOI lneanS coupled to said output means of said electronic oscilt0 prOVde thereto, after ampltCatOn, said direct later means; current potential for regulating said Vernier frea buifer amplifier means having input and Output means, qllEIlCy COnrOl element Within Said DSCllaOI 11163118 said input means thereof being coupled to said outthereby causing said oscillator means to maintain put terminal means of said electrical attenuation a Very Stable frequency Output signal, said input means for receiving a Signal from Said Oscillator means of said direct current amplifier and feedback means therethrough; means having a summation point for application of a series crystal phase shifting means comprising a first a rnOdulatOn Command Signal to provide frequency phase shifting means for sensing any deviations from rnOdulatiOn Of said Very stable frequency Output a predetermined frequency in signals passing there- 2O slgnal;

through and introducing a phase shift in said signals an Output termlnal Ineens COupled tO said Output means proportional to said deviations in frequency, said Of s'fud OsCllatOr Ineens, tO pfOVde said Very Stable phase shifting means having input and output means frequency. Ouiplll'. Signal. thereat fOI' utilization lll Subsaid input means thereof being coupled to said outsequent ClrCultlY- put means of said buffer amplifier means; a first tuned amplifier and limiter means having input References Cited by the Examiner and output means, said input means thereof being UNITED STATES PATENTS coupled to said output means of said first phase shift- 2,065,565 12 /1936 Crosby 33,1 1

ins means; 2,456,763 12/1948 Ziegler 331 17 a second phase shifting means for introducing a phase 2,752,512 5/1956 Sarratt 331 1 shift of predetermined amount into any signal passed 2,777,955 1/1957 Gabor 331 1 therethrough, having input and output means, said 3,010,073 11/1961 Meias 331 1 input means thereof being coupled to said output 3,021,492 2/1962 Kaufman 331 36 means 0f Said Oscillator means; 3,197,714 7/1965 prevailet 331 1 a second tuned amplifier and limiter means having input and output means, said input means thereof be- References Cited by the Applicant irlnlg coupled to said output means of said second phase UNITED STATES PATENTS s ifting means;

phase detector means having a first input means 2,297,409 9/1942 Hemeckecoupled to said output means of said first tuned 212981774 10/1942 Parkeramplifier and limiter means for receiving a first sig- 204591842 1/1949 RPYdennal therefrom, having a second input means coupled 7511518 6/1956 Plefceto said output means of said second tuned amplifier and limiter means for receiving a reference signal NATHAN KAUFMAN Primary Exammertherefrom, and having an output means for pro- I. KOMINSKI, Assistant Examiner. 

1. AN ELECTRONIC OSCILLATOR STABLIZATION SYTEM FOR PROVIDING AN OUTPUT SIGNAL HAVING A HIGH DEGREE OF FREQUENCY AND PHASE STABILITY COMPRISING: A HIGH QUALITY CRYSTAL CONTROLLED TRANSISTOR OSCILLATOR MEANS HAVING OUTPUT MEANS FOR PROVIDING A FREQUENCY CONTROLLED OUTPUT SIGNAL, AND HAVING INPUT MEANS FOR RECEIVING A SIGNAL FOR REGULATING A SOLID STATE VARACTOR DIODE ELEMENT WHICH COMPRISES A VERNIER FREQUENCY CONTROL ELEMENT IN SAID OSCILLATOR MEANS; AN ELECTRICAL ATTENUATION MEANS HAVING INPUT AND OUTPUT TERMINAL MEANS, SAID INPUT TERMINAL MEANS BEING COUPLED TO SAID OUTPUT MEANS OF SAID ELECTRONIC OSCILLATOR MEANS; A BUFFER AMPLIFIER MEANS HAVING INPUT AND OUTPUT MEANS, SAID INPUT MEANS THEREOF BEING COUPLED TO SAID OUTPUT TERMINAL MEANS OF SAID ELECTRICAL ATTENUATION MEANS FOR RECEIVING A SIGNAL FROM SAID OSCILLATOR MEANS THERETHROUGH; A SERIES CRYSTAL PHASE SHIFTING MEANS COMPRISING A FIRST PHASE SHIFTING MEANS FOR SENSING ANY DEVIATIONS FROM A PREDETERMINED FREQUENCY IN SIGNALS PASSING THERETHROUGH AND INTRODUCING A PHASE SHIFT IN SAID SIGNALS PROPORTIONAL TO SAID DEVIATIONS IN FREQUENCY, SAID PHASE SHIFTING MEANS HAVING INPUT AND OUTPUT MEANS, IN INPUT MEANS THEREOF BEING COUPLED TO SAID OUTPUT MEANS OF SAID BUFFER AMPLIFIER MEANS; A FIRST TUNED AMPLIFIER AN LIMITER MEANS HAVING INPUT AND OUTPUT MEANS, SAID INPUT MEANS THEREOF BEING COUPLED TO SAID OUTPUT MEANS OF SAID FIRST PHASE SHIFTING MEANS; A SECOND PHASE SHIFTING MEANS FOR INTRODUCING A PHASE SHIFT OF PREDETERMINED AMOUNT INTO ANY SIGNAL PASSED THERETHROUGH, HAVING INPUT AND OUTPUT MEANS, SAID INPUT MEANS THEREOF BEING COUPLED TO SAID OUTPUT MEANS OF SAID OSCILLATOR MEANS; A SECOND TUNED AMPLIFIER AND LIMITER MEANS HAVING INPUT AND OUTPUT MEANS, SAID INPUT MEANS THEREOF BEING COUPLED TO SAID OUTPUT MEANS OF SAID SECOND PHASE SHIFTING MEANS; A PHASE DETECTOR MEANS HAVING A FIRST INPUT MEANS COUPLED TO SAID OUTPUT MEANS OF SAID FIRST TUNED AMPLIFIER AND LIMITER MEANS FOR RECEIVING A FIRST SIGNAL THEREFROM, HAVING A SECOND INPUT MEANS COUPLED TO SAID OUTPUT MEANS OF SAID SECOND TUNED AMPLIFIER AND LIMITER MEANS FOR RECEIVING A REFERENCE SIGNAL THEREFROM, AND HAVING AN OUTPUT MEANS COUPLED TO SAID INPUT MEANS OF SAID OSCILLATOR MEANS FOR PROVIDING THERETO A DIRECT CURRENT POTENTIAL PROPORTIONAL TO THE AMOUNT OF DEVIATION FROM A PREDETERMINED RELATIVE PHASE DIFFERENCE BETWEEN SAID FIRST SIGNAL AND SAID REFERENCE SIGNAL, TO REGULATE SAID VERNIER FREQUENCY CONTROL ELEMENT WITH SAID OSCILLATOR MEANS THEREBY CAUSING SAID OSCILLATOR MEANS TO MAINTAIN A VERY STABLE FREQUENCY OUTPUT SIGNAL; AND AN OUTPUT TERMINAL MEANS COUPLED TO SAID OUTPUT MEANS OF SAID OSCILLATOR MEANS, TO PROVIDE SAID VERY STABLE FREQUENCY OUTPUT SIGNAL THEREAT FOR UTILIZATION IN SUBSEQUENT CIRCUITRY. 